The invention relates to an electrohydraulic actuating drive for valves, and more particularly for steam turbine valves.
There are already known various constructions of electrohydraulic drives for valves, among them such which are self-contained, that is, which include all the components needed for actuating the valve in response to electric signals. More particularly, such drives include, in addition to a hydraulic actuating cylinder-and-piston unit (hereafter cylinder for short), a storage receptacle for the hydraulic fluid, a hydraulic pump, an electric motor for driving the pump, and an electro-hydraulic transducer. These components are directly or indirectly mounted on the valve housing or on a lantern-shaped distancing and heat-dissipating element (hereafter called lantern) so mounted on the valve housing proper as to constitute a portion thereof.
An electrohydraulic actuating drive for valves of this type is known from the published German application DE-AS No. 11 83 760. In one of the constructions described therein, the electro-hydraulic transducer, the hydraulic actuating cylinder, the electric motor and the hydraulic pump are mounted on a plate which serves as a lid of the storage receptacle for the hydraulic fluid. The storage receptacle is, on its part, seated on a valve lantern, and the operating rod of the hydraulic actuating cylinder passes through the storage receptacle.
It is practically impossible to use the known electrohydraulic actuating drive for the actuation of turbine valves, such as regulating, rapid-closing or bypass valves of steam turbines. In such turbine valves, there must be, on the one hand, applied extremely high actuating forces at low actuating times, while, on the other hand, even the accommodation of the turbine valves themselves in the limited spatial conditions brings about difficulties and, therefore, small structural sizes and small structural weights are required from the corresponding actuating drives. Should the individual structural components be dimensioned in concordance with the actuating forces and the actuating times of turbine valves, the compact drive block of the known electrohydraulic actuating drive would be so large and heavy that its arrangement on the valve housing would no longer be possible.